The research of MEMS microphone chip has been continued for about 20 years, during this time, various microphone chips have been developed, such as piezo-resistive chip, piezo-electric chip, and capacitive microphones chip, in which the application of the capacitive MEMS microphone is most extensively. The capacitive MEMS microphone possesses advantages as follows: such as a mall volume, a high sensitivity, a better frequency characteristic, and a low noise. In addition, the capacitive MEMS microphone has a wide working temperature, it can work under a poor environment. The capacitive microphone can be distinguished into a double diaphragm capacitive structure and a signal diaphragm capacitive structure, and most of the capacitive microphones in which adopts the double diaphragm capacitive structure.
The capacitive silica-based MEMS microphone is generally consisted of a backplate and a vibrating diaphragm. The vibrating diaphragm has certain flexibility and it can be vibrated by virtue of air. The backplate has certain rigidity and fully defines a plurality of holes which are so called acoustic holes. Air can penetrate through the plurality of holes to enable the vibrating diaphragm to vibrate, and the backplate will not vibrate accompanying to the vibrating diaphragm. A plate capacitor is constituted by the backplate and the vibrating diaphragm, a voice drives the flexible vibrating diaphragm to vibrate by the air, thereby changing the capacitance value of the plate capacitor. The change of the capacitance value generates an electrical signal which can be detected by an external circuit, thereby a transition from a voice signal to an electrical signal can be achieved. The MEMS device, including silica-based microphone, is generally produced by an integrated circuit manufacturing technology. The silica-based microphone has a wide application prospect in the fields such as hearing-aid and mobile communication equipment.
For the capacitance silica-based MEMS microphone, the flexibility of the vibrating diaphragm determines a sensitivity of the microphone, because a greater flexibility results to a greater longitudinal displacement of the vibrating diaphragm, and a greater electrical signal is generated. However, the softer of the vibrating diaphragm, the easier it is adhered to the backplate, causing the MEMS microphone not to work correctly, and a yield is severely affected. There are various methods to avoid the adhesion between the backplate and the vibrating diaphragm, at present, a more efficient method is to produce anti-adhesion bulges, however, the process steps are increased, and a cost is increased. Another method is to excavate a central region of the backplate. Because a central region of the vibrating diaphragm has a highest mechanical sensitivity and a greatest deformation, it can be easily adhered to the backplate. When the central region of the backplate is excavated, the adhesion between the vibrating diaphragm and the backplate can be efficiently avoided. However, the central region of the vibrating diaphragm has the highest mechanical sensitivity, and the edges have a lower mechanical sensitivity, when the central region of the backplate is excavated, the central position of the vibrating diaphragm is wasted, reducing a sensitivity of the MEMS microphone